1. Field of the Invention
The present invention relates to a nonvolatile semiconductor memory device using a variable resistive element of which resistance is stored as data.
2. Description of the Related Art
Electrically erasable programmable nonvolatile memories include a flash memory as well known in the art, which comprises a cell array of NAND-connected or NOR-connected memory cells having a floating gate structure. A ferroelectric memory is also known as a nonvolatile fast random access memory.
On the other hand, technologies of pattering memory cells much finer include a resistance variable memory, which uses a variable resistive element in a memory cell as proposed. Known examples of the variable resistive element include a phase change memory device that varies the resistance in accordance with the variation in crystal/amorphous states of a chalcogenide compound; an MRAM device that uses a variation in resistance due to the tunnel magneto-resistance effect; a polymer ferroelectric RAM (PFRAM) memory device including resistive elements formed of a conductive polymer; and a ReRAM device that causes a variation in resistance on electrical pulse application (Patent Document 1: JP 2006-344349A, paragraph 0021).
The resistance variable memory may configure a memory cell with a serial circuit of a Schottky diode and a resistance variable element in place of the transistor. Accordingly, it can be stacked easier and three-dimensionally structured to achieve much higher integration as an advantage (Patent Document 2: JP 2005-522045A).
The methods of writing data to such the resistance variable memory include one, which comprises once clearing all memory cells. This method has an advantage because it is sufficient to write data only to the memory cell of question without the need for considering data stored immediately before. This method, however, can not allow the resistance variable memory to sufficiently exert the performance of the operating speed.